1. Field of the Invention
The present invention relates to a plasma display panel, and more particularly, to a method for operating a plasma display panel (PDP), in which a pulse applied to an electrode in the PDP is controlled according to a gray scale of a picture to be displayed.
2. Background of the Related Art
Of the different flat board type display devices, the PDP is paid attention as a large sized panel because the PDP has many advantages suitable for fabricating a large sized display device.
Most typically, the PDP is provided with 3 electrodes and is driven by an AC voltage, called as an AC surface discharge type PDP. FIG. 1 illustrates a perspective view of a discharge cell of a related art AC PDP of surface discharge type having 3-electrodes.
Referring to FIG. 1, the discharge cell is provided with a scan electrode 12Y and a common sustain electrode 12Z formed on a front substrate 10, and an address electrode 20X formed on a back substrate 18.
There are a front dielectric 14 and a protective layer 16 stacked on the front substrate 10 having the scan electrode 12Y and the common sustain electrode 12Z formed in parallel. The front dielectric 14 is provided for accumulation of wall charge generated in plasma discharge.
The protective layer is provided for protecting the front dielectric 14 from damage caused by sputtering of the plasma discharge, and enhancing a secondary electron emission efficiency. In general, the protective layer 16 is formed of magnesium oxide MgO.
There are a back dielectric 22 and a barrier rib 24 on the back substrate 18 having the address electrode 20X formed thereon. There is a phosphors 26 coated on surfaces of the back dielectric 22 and the barrier rib 24. The address electrode 20X is formed in a direction perpendicular both to the scan electrode 12Y and the common sustain electrode 12Z. The phosphors 26 are excited by UV ray emitted in the plasma discharge, to emit one of red, green, and blue visible light. There is an inert gas injected into a discharge space between the two substrates and the barrier rib.
Referring to FIG. 2, there are a matrix of the discharge cells arranged in the PDP.
Referring to FIG. 2, the discharge cell 1 has a scan electrode line Y1, - - - , or Ym and a sustain electrode line Z1, - - - , or Zm running in parallel, and the discharge cell is provided in every part the two electrode lines Y1, - - - , and Ym and Z1, - - - , and Zm cross the address electrode lines X1, - - - , and Xn.
The scan electrode lines Y1, - - - , and Ym are operative in a sequence, and the common sustain electrode line Z1, - - - , and Zm are operative in common. The address electrode lines X1, - - - , Xn are operative with odd numbered lines and even numbered lines divided.
In the related art AC PDP of surface discharge type having 3-electrodes, an operation time period for displaying a particular grey scale of a frame is divided into sub-fields. In each of sub-field duration, a number of times of light emissions proportional to a weight value of a video data is progressed to display a grey scale.
As an example, referring to FIG. 3, when a picture of 8 bit data is displayed in 256 grey scales, one frame display duration (for an example, {fraction (1/60)} seconds=approx. 16.7 msec) of each discharge cell 1 is divided into 8 sub-fields (SF1-SF8).
Each of the sub-fields (SF1-SF8) is again divided into a reset duration, an addressing duration, and a sustain duration, and each sustain duration of the sub-fields (SF1-SF8) has a time weight variably given in a ratio of 2N (where N=0, 1, 2, 3, - - - , 7). That is, time weights in a ratio of 1:2:4:8:16:32:64:128 are given to the sub-fields SF1-SF8 starting from a first sub field SF1 to an eighth sub-field SF8.
FIG. 4 illustrates operation waveforms applied to respective electrodes in each sub field in FIG. 3.
Referring to FIG. 4, each of the sub fields in the related art PDP is operated, with the sub field divided into a reset duration, addressing duration, a sustain duration, and an erasure duration.
The reset duration is a duration for initializing the discharge cell. The address duration is a duration for making a selective address discharge according to a logical value of the video data. The sustain duration is a duration for sustaining an address discharge in a discharge cell. The erasure duration is a duration for erasing all discharges sustained in all the discharge cells.
In the erasure duration, a erasure pulse E is applied to the common sustain electrode Z, to erase the sustain discharge.
In the reset duration, a reset pulse RP is applied to the scan electrode Y to cause reset discharge at all discharge cells. Once, the reset discharge is occurred at all discharge cells, all the discharge cells are initialized.
In the addressing duration, a scan pulse SP is applied to the scan electrodes Y in succession, and a data pulse DP synchronous to the scan pulse SP is applied to the address electrodes X. In this instance, in the discharge cells having the scan pulse SP and the data pulse DP applied thereto, address discharges are occurred.
In the sustain duration, a sustain pulse SUSP1 or SUSP2 is applied to the scan electrodes Y and the common sustain electrodes Z, alternately. Upon application of the sustain pulse SUSP1 or SUSP2 alternately, sustain discharge is occurred at the discharge cells the address discharge is occurred therein for a preset duration.
The sustain pulse SUSP1, or SUSP2 has a pulse width in a range of approx. 2-3 xcexcs. The sustain pulse S applied to the scan electrode Y at first has a pulse width in a range of 5 xcexcs so as to cause the sustain discharge easily.
A number of the sustain pulses SUSP1, or SUSP2 is increased for each sub field separately for displaying a picture in preset grey scales. For an example, the first sub field has two sustain pulses SUSP1 or SUSP2, and the second sub field has four sustain pulses SUSP1 or SUSP2. The third sub field has eight sustain pulses SUSP1 or SUSP2. Thus, the related art PDP controls the number of sustain pulses SUSP1 SUSP2, for meeting required grey scales.
In the meantime, referring to FIG. 5, for obtaining a stead distribution of optical waveforms, it is required that at least 5 sustain pulses SUSP1, or SUSP2 are applied to the scan electrode Y and the common electrodes Z.
In more detail, an initial sustain pulse SUSP1 or SUSP2 causes a weak sustain discharge. Then, after an adequate wall charge is formed by several times of following sustain discharges, steady sustain discharges are occurred. Thus, the initial sustain discharge can not provide an adequate luminance.
Due to such discharge characteristics, sub fields that are required to display pictures in low grey scales can not obtain luminances consistent to the grey scales. In other words, the instable sustain discharge causes an erratic discharge in displaying a picture of a low grey scale.
Particularly, when an entire screen is displayed in low grey scales, the erratic discharge causes blinking of the screen, that deteriorates a picture quality. This blinking becomes the worse, as the addressing duration is the shorter, i.e., when the wall charge is not formed adequately during the addressing.
In the meantime, a high voltage may be applied in the addressing duration for prevention of the picture quality deterioration. That is, a voltage high in proportion to a reduction of the addressing duration may be applied for forming an adequate wall charge at the discharge cell. However, the application of the high voltage in the addressing duration requires a high voltage data drive IC (Integrated Circuit). Moreover, the high voltage data drive IC, not only consumes much power, but also high installation cost. In conclusion, what is required is a method for displaying a picture of lower grey scales while the voltage in the related art is kept.
Accordingly, the present invention is directed to a method for operating a PDP that substantially obviates one or more of the problems due to limitations and disadvantages of the related art.
An object of the present invention is to provide a method for operating a PDP, which permits to obtain an adequate luminance for grey scales required at sub fields that are required to display pictures in low grey scales, and suitable for displaying a picture of lower grey scales without deterioration of the picture without addition of an IC.
Additional features and advantages of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.
To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, the method for operating a PDP having three electrodes, the PDP for displaying one frame which includes a plurality of sub-fields each having a reset period, an addressing period, and a sustain period in view of time, the method includes the steps of applying a fixed number of pulses in a fixed frequency in each period for displaying an image of a particular grey scale, and adjusting a number of pulses and/or a frequency applied in each period for displaying an image having a grey scale different from the particular grey scale.
More preferably, for a part of sub-field (A) to be displayed in a lower grey scale image, pulses of a lower frequency are applied to a scan electrode in the addressing period of the sub-fields (A).
For a part of sub-fields (A) to be displayed in a relatively lower grey scale image, a number of pulses more than a regular number are applied to the scan electrode and the sustain electrode alternately in the sustain period of the sub-fields (A).
For a part of sub-fields (A) to be displayed in relatively lower grey scale images, pulses of a lower frequency are applied to the scan electrode and the sustain electrode alternately in the sustain period of the sub-fields (A).
Of the sub-fields of the frame, a plurality of pulses are applied to the scan electrode in the reset period of the first sub-field.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.